1. Field of the Invention
This invention relates to a novel polymeric peroxide possessing three types of peroxide groups differing in thermal decomposition rates. This invention further relates to a polymerization initiator having the polymeric peroxide as an active agent for a monomer having a vinyl group and to a method for the production of a block copolymer by polymerizing monomers having a vinyl group in two stages by the use of the polymeric peroxide.
2. Description of the Prior Art
Known polymeric peroxides having at least two peroxide groups in the molecular unit include some which have peroxide groups having the same thermal decomposition rate and some which have peroxide groups having different thermal decomposition rates. As polymeric peroxides of the former type, there have been reported a diacyl type polymeric peroxide formed by the reaction of phthalic acid chloride with sodium peroxide [Berichte der Deutschen Chemischen Gesellschaft, Vol. 27, p. 1,510 (1894)], a diacyl type polymeric peroxide formed by the reaction of an oxalyl chloride with sodium peroxide [Journal of the American Chemical Society, Vol. 68, p. 534 (1946)], and diacyl type polymeric peroxides represented by the following general formula and obtained by the reaction of an aliphatic dibasic acid chloride with sodium peroxide [Chemical Abstracts, Vol. 60, 5293d and 10892e (1964)]. ##STR5## (wherein n is in the range of from 2 to 10 and x is in the range of from 16 to 35).
As the polymeric peroxides of the latter class, there have been reported a polymeric peroxide obtained by the reaction of a substituted succinic acid chloride and p-diisopropylbenzene dihydroperoxide [Journal of Organic Chemistry, U.S.S.R., Vol. 13, No. 1, p. 210 (1977)] and polymeric peroxides having the following two groups bound to each other [Japanese Patent Public Disclosure SHO 59(1984)-8727]. ##STR6## (wherein X.sub.1 stands for a --CH.sub.2 --CH.sub.2 -- group or a --C.tbd.C-- group).
Generally, polymeric peroxides are useful as a polymerization initiator for the production of a block copolymer from a vinyl type monomer. To be more specific, the production of a block copolymer by the use of a polymeric peroxide is effected by polymerization involving the following two stages.
(1) In the first stage, a vinyl type monomer is polymerized with a polymeric peroxide as a polymerization initiator to form a first-stage polymer having a fixed amount of the peroxide group of the polymeric peroxide chemically bound to a polymer chain.
(2) In the second stage, the first-stage polymer possessing the peroxide group is purified, if necessary, then mixed with a vinyl type monomer of a type different from that of the first-stage polymer, and subjected to a second-stage polymerization using the peroxide group chemically bound to a polymer chain in the polymer as a polymerization initiator to give rise to a block copolymer of the two vinyl type monomers.
The first-stage polymerization, however, does not easily produce the polymer possessing the peroxide in a high yield. In order for the peroxide group of the polymeric peroxide to be chemically bound to the polymer chain without fail, the radical for initiating the polymerization is required to be of a structure substituted with at least one peroxide group. The polymer which is obtained by the ordinary polymerization mechanism using the radical of the kind described above possesses a peroxide group at the terminal thereof. If the radical to be used is of the ordinary type possessing no peroxide group, the produced polymer has no peroxide group at the terminal thereof. Thus, the second-stage polymerization is incapable of producing a block copolymer. If the produced polymer possesses a peroxide group at the terminal, the thermal decomposition property of the peroxide group must be such as to avoid generating a radical under the conditions of the first-stage polymerization. Otherwise, the first-stage polymerization causes the terminal peroxide group to generate a radical which induces a polymerization reaction. As a result, the first-stage polymerization produces a polymer containing no peroxide group.
For the purpose of enabling the second-stage polymerization to produce the block copolymer in a high yield, the first-stage polymerization must exhibit as high selectively for the polymer possessing a peroxide group as possible. For this reason, the selection of the polymeric peroxide to be used becomes an important factor.
In all of the known polymeric peroxides mentioned above, the two or more peroxide groups present in the molecular units have relatively small differences or no difference in their thermal decomposition rates. When the block copolymerization is carried out using such a polymeric peroxide, it produces the block copolymer only in a low yield.
A need has therefore been felt for the development of a polymeric peroxide which possess in the molecular unit thereof two or more peroxide groups exhibiting widely different thermal decomposition rates.